The present invention relates to an apparatus and a plant for separating two immiscible liquids of different specific gravities.
The invention is more particularly applicable to the deoiling of cleaning agents of industrial use such as especially industrial cleaning solutions.
Industry in general and more particularly the mechanical industry uses an enormous quantity of cleaning agents for scouring or clearing and washing manufactured parts and, both for economy purposes and for meeting the regulations governing oil discharge into surface-, underground- and sea-waters, it became absolutely essential to treat as thoroughly as possible, in particular, the waste cleaning solutions and the washing water from industrial cleaning machines, the purpose of the treatment being, on the one hand, to limit pollution and, on the other hand, to afford separate recovery of the oils and scouring agents for re-use thereof.
Separation of the two liquid phases of an emulsion or a suspension is a so-called "breakage" operation which can be effected either by a chemical or by a physical process, the method used according to the invention being related to the latter process and using the physical phenomenon of coalescence between the fine oil droplets suspended in the scouring agent to be purified. It should be remembered that coalescence is the ability of the particles in a finely divided liquid to join together so as to reconstitute a continuous liquid phase.
Of course, the use of this physical phenomenon for separating two immiscible liquids is already known and practised in numerous plants designated to break a dispersion of oil in an aqueous phase. In particular, separation apparatuses are known which include parallel, slanted banks of coalescence plates, between which banks the scouring agent to be deoiled flows, said coalescence plates being provided with corrugations on certain separators.
Separating apparatuses are also known wherein the coalescence and settling phenomena are associated, sometimes with an attempt to increase the separation speed by imparting a rotary motion to the mixture to be purified introduced into the separator.
In all these known apparatuses, the coalescence of the oil droplets generally occurs in counter flow to the liquid phase wherein the droplets are suspended, this resulting in a low separation efficiency and requiring the use of over-sized plants to afford a sufficient recovery output. Moreover, in the aforementioned separators, the rotary motion of the liquid mixture fed to the apparatus creates an internal turbulence which causes permanent mixing of the phases and counteracts the natural coalescence of the oily droplets. The result is a substantial reduction in efficiency which has to be compensated by several runs of the mixture through the separator, to the prejudice of the plant output.
Thus, more precisely, there are known in the prior art:
U.S. Pat. No. 1,920,565 relating to a process and an apparatus for the separation of oil-water mixtures.
The apparatus shown in this U.S. patent consists of a first separator A wherein a first separation of oil from water is effected. The residue that still contains some oil is fed to an apparatus B and contacted with a light oil that may or not contain an emulsion-controlling agent such as a calcium oleate. This mixture in then separated in a second separator C into pure water and oil.
The apparatus shown in this reference requires both addition of light oil and a mixing or stirring chamber together with stirring means.
DE OS No. 2,652,632 which describes a plant for recovering oil including notably an elongate ducting 42 extending along the periphery of a tank 32, said duct 42 having a plurality of apertures 34 in communication with tank 32. A pipe 18 feeds the oil/water mixture to be separated to ducting42 and the mixture is separated by flowing through coalescence means 48.
This plant is applied to a ship
FR Pat. No. 577,288 which describes an apparatus to effect separation between petroleum and water. This apparatus consists of a U-shaped duct including two legs a and b. This document teaches an adjustment in height along leg b by means of a sleeve g.
U.S. Pat. No. 2,342,950 which describes an apparatus for treating liquids such as oil emulsions or mixtures comprising cold oil, oil emulsions and water by heating the liquid, evolving those components of the liquid as are easy to gasify, then separating the water from the oil in a calm area.
FR patent application No. 74/41,972 issued under No. 2,255,931 which describes an oil separating device including a separation chamber 16 wherein the rising oil flow past baffles 26. The oil is discharged through an overflow 33 located at an adjustable level.
GB Pat. No. 787,804 which describes a method and an apparatus for separating oil from ballast water in tanks of oil tankers. According to this GB patent, provision is made to pump the oil and water mixture until an oil-free surface is obtained, while aerating the mixture of the two liquids to facilitate separation thereof.
GB Pat. No. 205,935 which describes a method and an apparatus for separating liquids of different specific gravities, especially an oil and water mixture.
The apparatus mentioned in this GB Pat. No. 205,935 includes a tank D.sup.1 wherein the water-oil mixture to be separated is fed. Said mixture flows through a pipe D to be directed against a deflecting plate D.sup.2. A main separation chamber A.sup.1 and a tubular casing B are permanently full of liquid, chamber A being full of water while casing B is full of oil. The water flows through pipe E and is directed to tank F.sup.1. The oil flows into receptacle B.sup.1 and is discharged through overflow B.sup.2.
FR Pat. No. 1,459,465 which describes an apparatus for separating oil from a spent oil and water mixture.
The apparatus comprises a tank 1 wherein the mixture to be separated is fed through a pipe 4. The mixture is discharged into portion 3 of tank 1 through an annular pipe 5 provided with perforations; the mixture being discharged along the wall of a baffle 6. This action is continued until the mixture reaches the discharge pipe 23. The floating oil is then removed through pipe 23. This FR Pat. No. 1,459,465 relates to an apparatus whereof the principle is different from that of the present invention; indeed, it will be appreciated that the conical surface converges (diminishes in area) downwards, i.e. in opposite direction to the natural motion of the oil particles which tend to rise.
Consequently, the coalescence is not promoted by the reduction in area.
Moreover, the oil particles are first set into motion downwards, while the gravity separation occurs according to the present invention, as described hereinafter, due to the fact that these particles rise immediately as they enter the working chamber.
In the apparatus according to FR Pat. No. 1,459,465, the oil drops are subjected to an artificial, unfavourable motion, which tends to carry them downwards with the dense liquid flow.
The object of the present invention is therefore to provide an apparatus for continuous separation as well as a plant incorporating said apparatus and allowing a very extensive continuous separation to be effected between two immiscible liquids of different specific gravities with a very high efficiency under reduced space requirements.